Add time:09/27/2019         Source:infona.pl

Here we provide evidence that the form of carbon compound and O 2 concentration exert an inter-related regulation on the production and reduction of N 2 O in soil. 6.7 mM d-glucose, 6.7 mM D-mannitol, 8 mM L-glutamic acid or 10 mM butyrate (all equivalent to 0.48 g C l −1 ) were applied to slurries of a sandy loam soil. At the start of the experiment headspace O 2 concentrations were established at ∼2%, 10% and 21% O 2 v/v for each C treatment, and 2 mM K 15 NO 3 (25 atom % excess 15 N) was applied, enabling quantification of 15 N–N 2 production, 15 N–(N 2 O-to-N 2 ) ratios and DNRA. The form of C compound was most important in the initially oxic (21% O 2 v/v) soils, where addition of butyrate and glutamic acid resulted in greater N 2 O production (0.61 and 0.3 μg N 2 O–N g −1 soil for butyrate and glutamic acid, respectively) than the addition of carbohydrates (glucose and mannitol). Although, there was no significant effect of C compound at low initial O 2 concentrations (∼2% O 2 v/v), production of 15 N–N 2 was greatest where headspace O 2 concentrations were initially, or fallen to, ∼2% O 2 v/v, with greatest reduction of N 2 O and lowering 15 N–(N 2 O-to-N 2 ) ratios (∼0–0.27). This may reflect that the effect of C is indirect through stimulation of heterotrophic respiration, lowering O 2 concentrations, providing sub-oxic conditions for dissimilatory nitrate reduction pathways. Addition of carbohydrates (glucose and mannitol) also resulted in greatest recovery of 15 N in NH 4 + from applied 15 N–NO 3 − , indicative of the occurrence of DNRA, even in the slurries with initial 10% and 21% O 2 v/v concentrations. Our 15 N approach has provided the first direct evidence for enhancement of N 2 O reduction in the presence of carbohydrates and the dual regulation of C compound and O 2 concentration on N 2 O production and reduction, which has implications for management of N 2 O emissions through changing C inputs (exudates, rhizodeposition, residues) with plant species of differing C traits, or through plant breeding.

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